It is known that solid cyanuric chloride readily agglomerates when in finely divided form. In order to eliminate the consequent problems during storage and further processing, DE-AS 11 34 999 teaches the addition of flow auxiliaries to the finely divided cyanuric chloride, selected from the range of finely divided silicon dioxide, titanium dioxide, aluminium oxide, aluminium silicate and calcium silicate, in a quantity of 0.3 to 3 wt. %. Only one pyrogenically produced silica, namely AEROSIL.RTM. (Degussa-Huls AG, Germany) is mentioned among the silicas stated in this document as flow auxiliaries. No suggestion is made to use silicas of other origins.
As is disclosed by DE-AS 28 39 384, using a hydrophobic pyrogenic or hydrophobic precipitated silica makes it possible not only to improve the flowability of cyanuric chloride, but also to counteract the unwanted hydrolysis of cyanuric chloride which occurs during storage and in-plant handling. Hydrolysis products formed during the storage and conversion of cyanuric chloride reduce the quality and/or yield of the reaction products.
In the process according to EP-A 0 416 584, an attempt was made to improve the flowability of solid cyanuric chloride by subjecting the cyanuric chloride to shear forces in a kneader or mixer while heating it to a temperature below the melting point. However, it was found (see Comparative Examples) that the reactivity of such products is reduced. Due to the inadequate storage stability of products treated in this manner, this process has not become established in practice, such that most commercial products still contain a hydrophilic pyrogenic silica or a hydrophobic pyrogenic or precipitated silica as a flow auxiliary.
A substantial disadvantage not only of all hydrophilic pyrogenic silicas as well as hydrophobic pyrogenic silicas but also of hydrophobic precipitated silicas is the high cost thereof, due to the production process. Specialist manufacturers are accordingly interested in lower cost alternatives, wherein these alternatives must exhibit an at least equivalent range of properties.